Enter what you measured and the known accepted value — get the percent error and the signed absolute error side by side.
Percent error measures how far an experimental or measured value is from a known, accepted true value, expressed as a percentage: |experimental − true| / |true| × 100. It's the standard way labs and classrooms report how accurate a measurement was against a known reference.
Percent error is meant to report the size of the miss, not its direction — the absolute value strips the sign so a measurement that came in high and one that came in low by the same amount get the same percent error. This calculator also reports the signed absolute error (experimental − true) separately, so the direction isn't lost — just kept out of the percentage itself.
There's no single universal cutoff — it depends entirely on the field, the instrument, and what's being measured. A physics lab timing a pendulum with good equipment might target under 1–2%, while some biology or chemistry experiments with more natural variability routinely accept 10% or higher as reasonable. Compare your result against what's typical for your specific experiment rather than assuming a fixed threshold applies everywhere.
No, and mixing them up is a common mistake. Percent error compares a measured value against a known, accepted true value — that's what this calculator computes. Percent difference compares two experimental values to each other when neither one is a trusted reference, typically as the absolute difference divided by the average of the two values, times 100. Use percent error whenever you have a correct answer to check against; reach for percent difference only when comparing two measurements with no accepted "true" value between them.
Worked example: a measured value of 48 against a true value of 50: absolute error = 48 − 50 = −2, and percent error = |48 − 50| / |50| × 100 = 2/50 × 100 = 4%. The negative absolute error shows the measurement came in low; the percent error strips that sign to report the size of the miss.